Study of Ultra-Thin Silicon Micropillar Based Vapor Chamber

Silicon vapor chamber has drawn much attention in recent years, owing to its mature microfabrication process, accurate control over its geometries, direct integration with semiconductor devices that can eliminate the thermal interface resistance and prevent thermal expansion mismatch.In this paper, micropillar wicks that can generate excellent capillary performance and possess high permeability was adopted as the evaporator and adiabatic wick structure.Ultra-thin vapor chambers with thickness of only 1.25 mm were fabricated, the total size of the vapor chamber was 4 cm×4 cm×1.25 mm.As essential parts of a vapor chamber, the geometric sizes of the micropillars at evaporator and adiabatic regions were optimized.Based on the Brinkman equation derived dryout heat flux model, the optimal geometric combinations for evaporator and adiabatic regions were d =17.4 µm, h = l =30.6 µm and d =15 µm, h = l =30.6 µm respectively.Actual sizes after micro fabrication was d =18.9 µm, h =31.3 µm, l =30.6 µm and d =15.8 µm, h =31.3 µm, l =30.6 µm for evaporator and adiabatic regions respectively.Performance comparison between optimized and nonoptimized samples has shown that the optimized sample performed best, which can dissipate a high heat flux of 98.1 W/cm 2 before dryout.The deviation between model predicted and experimentally measured dryout heat flux was only 11.2 %, which validated the model with high accuracy.Effective thermal resistance of various samples was also studied.A smallest effective thermal resistance of 0.53 K/W can be obtained.Effective thermal resistance was found to decrease with heat flux before dryout while a reverse trend was observed after dryout.The vapor chamber was also found to have a good temperature uniformity.The largest temperature difference was only 9.6 C at very high heat load of 98.1 W. This paper demonstrated significant insights into the investigation of silicon vapor chamber, and can be used as useful design guidance for micropillar based vapor chambers.